Just tested it again just a bit ago and it happened again.
Had 13 Armor used the ability and it killed 3 monsters but lowered my armor to 6, just for info it was in the Browser version.
Hope it helps!
Got it! In the browser version this was done on purpose, the ability seemed too strong. This has been fixed in the demo version - https://store.steampowered.com/app/3828710/Dungeon_Raid_Dem
